Field of the Invention
The present invention is related to a robot actuator position control method, and particularly to a robot actuator position control method for setting coordinate data for a target position of the actuator at each assembly operation in the course of assembling a workpiece into an objectpiece transferred by an assembly line.
Description of the Prior Art
In order to move the center point of the workpiece to a desired position by a robot hand or arm (hereinafter, called an actuator), the coordinate data for the desired position should be determined prior to a specific assembly operation.
In one method for determining the coordinate data for the desired position, an operator may move the actuator of the robot to the desired position by means of a teaching box, and then set the coordinate data for the position (hereinafter, called a target position) at which the actuator is currently located. Another method for determining the coordinate data for the target position is for the operator to set the coordinate data for the target position in the form of numeral data or a robot language by means of a key board input device. The operator may also determine the coordinate data for the target position by setting the coordinate data by means of another system and then transmitting the coordinate data to the robot system.
The coordinate data for the target position of the robot actuator set by the methods described above are maintained until an error in the assembly operation is detected.
However, there is a problem in that when there is a defect in the robot mechanism or the controller for the robot system, an undesirable deviation may occur between the target position and the actual position of the actuator of the robot. When this occurs, it becomes necessary to again set the coordinate data for the target position for the actuator and this interrupts the assembly operation.
On the other hand, a deviation between the target position for the objectpiece and the actual position to which the objectpiece is transferred by the assembly line may also occur due to a defect in the robot mechanism or the robot system controller. Accordingly, when both deviations described above occur concurrently, the entire deviation exceeds an acceptable limit for the robot system, thereby frequently interrupting the assembly operation.
A typical example of prior art for a robot position control system is disclosed in U.S Pat. No. 4,659,971. The invention disclosed in the U.S Patent has an object to substantially simplify the operation for specifying the operating position and the actuator direction when an operation is carried out at a plurality of operating positions of the same member to be assembled placed in a plurality of places in the same robot system. However, a method for reducing errors in the assembly operation due to a defect in the robot mechanism or the robot system controller is not disclosed in the U.S Patent.